Since our entire climate system is fundamentally driven by energy from the sun, it stands to reason that if the sun's energy output were to change, then so would the climate. Since the advent of space-borne measurements in the late 1970s, solar output has indeed been shown to vary. With now 28 years of reliable satellite observations there is confirmation of earlier suggestions of an 11 (and 22) year cycle of irradiance related to sunspots but no longer term trend in these data. Based on paleoclimatic (proxy) reconstructions of solar irradiance there is suggestion of a trend of about +0.12 W/m2 since 1750 which is about half of the estimate given in the last IPCC report in 2001. There is though, a great deal of uncertainty in estimates of solar irradiance beyond what can be measured by satellites, and still the contribution of direct solar irradiance forcing is small compared to the greenhouse gas component. However, our understanding of the indirect effects of changes in solar output and feedbacks in the climate system is minimal. There is much need to refine our understanding of key natural forcing mechanisms of the climate, including solar irradiance changes, in order to reduce uncertainty in our projections of future climate change.